Hydrothermal Liquefaction of Galdieria sulphuraria Grown on Municipal Wastewater

Abstract. Subcritical hydrothermal liquefaction uses high temperatures (270-350°C) and high pressures (80-173 bar) to produce bio-crude oils that can be upgraded to liquid transportation fuels. In this study, two strains of Galdieria sulphuraria, an acidophilic, mixotrophic red microalgae, were cultivated on effluent from primary settling tanks at a municipal wastewater treatment plant. Samples were concentrated to 5 and 10 wt.% slurries after harvest and converted by hydrothermal liquefaction in a 1.8 L batch reactor. Reaction conditions included temperatures of 310, 330 and 350°C, and hold times of 5, 30 and 60 minutes. Yields and product properties were compared to those of hydrothermal liquefaction of Galdieria sulphuraria grown on media. Total oil yields were low (11-18 wt.%) and char yields were high (28-36 wt.%) compared to those from HTL of the algae grown on media (27-35 wt.% oil and 10-13 wt.% char), likely due to the higher ash content and lower lipid content of the algae grown on wastewater. The bio-crude oil, char, and aqueous phase samples were characterized to complete mass, energy and nutrient balances to characterize the tradeoffs in the algae growth and conversion systems for energy and nutrient recovery.